HDPE Pipes

Polymer grade Before After % Mass swell % Dimensional swell 

As far as can be ascertained, no performance standards exist for this product. In the absence of such standards, the existing standards for automotive vehicles were used as guidelines. By using the most stringent standard, the SHED test, a petrol permeation rate of approximately 3.3 g/m2 for 24 h at 40°C can be estimated. With a single-fluorination treatment a pipe already exceeds this standard with a steady state permeation rate of 1.7 g/m2 per 24 h at 50°C. Since it is a known fact that permeability increases drastically with a rise in temperature, a permeability ofless than 0.17 g/m2 per 24h at 30°C is expected for a single fluorination treatment. 

Petrol permeation through HDPE pipe at 50°C Pipe = Type 4 Class 10 petrol 90 octane high altitude. 

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The original perforated collector pipes in landfills were made of concrete like those used in highway underdrain systems. As landfills became higher, the strength of such pipes became inadequate. Today, perforated PVC pipes are commonly used, as are HDPE pipes. New regulations require that all materials be tested for chemical resistance as part of the permit-approval process. 

This problem was most effectively solved by fluorination of the HDPE pipes. A fluorinated layer thickness, one-fifth of that used for fluorinated LLDPE fuel tanks, was used initially. As can be seen from Figure 16.1, a significant... 

HDPE pipes are used for transporting water, sewer wastes, and gas they are also widely used in the chemical industry. Other significant applications include wire and cable coatings, foam, insulation for coaxial and communication cables, as well as those areas where high resistance to oil and chemicals is desirable. 

This expression shows that the critical circumferential stress falls with increasing pipe diameter D. This relation and the difficulty to extrude and keep in shape plastic pipes with large wall thicknesses s limit their upper size (at this time the largest external diameter of an extruded (HDPE) pipe is 1400 mm). 

The application areas of bimodal polyethylenes are the same as for corresponding uni-modal resins. However, improved product property combinations, such as stiffness-impact balance, result in products with higher performance. For example, without bimodal polyethylene and control over the MWD and comonomer incorporation, development of HDPE pipe materials with higher pressure classification would not have been possible [15, 16]. Another new opportunity is material reduction (source reduction) without compromising the properties of the ready-made plastic products. Depending on the end use, e.g. in film application a thickness reduction of 10-30% is possible. 

In industry, hydrostatic pressure testing of pipes is still widely used to assess their resistance to this type of failure. Typical results are shown in Fig. 6 [57, 58], where failure times of HDPE pipes are given as a function of the circumferential (or hoop) stress. At relatively high stresses, ductile failure is observed (stage I) although deformation is initially homogeneous, small local variations (arising from variations in the specimen thickness, for exam-... 

Fig. 6 Durability diagram for HDPE pipes under internal pressure, showing hoop stress vs. the time to fail at different temperatures, along with the regimes of ductile failure (I) and brittle failure (II) [57, 58]...

Tomboulian et al. (2002) has reported that butylated hydroxytoluene (BHT) can impart a "burnt plastic" odor and is an additive in HDPE pipes. Quinone may be derived from BHT due to interactions with residual chlorine in pipes (Anselme et al., 1985). Yam et al. (1996) reported that antioxidants, such as vitamin E, Irganox 1010, and BHT, contributed to off-flavors in water. Vitamin E yielded less off-flavor, possibly due to lower aldehyde and ketone concentrations. Extrusion temperatures over 280 °C and exposure time for melt contributed to more oxidation of LDPE films and higher intensities of off-flavors in water in contact with LDPE with different antioxidants (Andersson et al., 2005). 

Manufacturing-Plastic Pipe Products PVC HDPE Pipes Fittings... 

Plastics Pipe Institute, 100-Year Design Life Cited for Corrugated HDPE Pipe, PT, June 2003. 

Fig. 3.70 CM-AFM height images of the cross-section of etched specimens transverse to the extrusion direction of extruded HDPE pipes (a) cooled edge (b) midway between the cooled edge and the middle (c) middle (d) non-cooled edge. In all images, the cooling direction is from the bottom to the top. Scan size 40 x 40 pm2. Gray scale for the feature heights black = 0.0 nm white = 1.20 pm. Reprinted with permission of John Wiley Sons, Inc. from [148], Copyright 1997. John Wiley Sons, Inc.

Peroxides are mainly used for the production of HDPE pipes. The basic process consists of three steps. 

Vinyl functional silanes have been used for over 35 years to crosslink polyethylene. The most common commercial products using this crosslinking technology are crosslinked PE insulations for the global wire and cable market [11] and crosslinked HDPE pipes for potable water and natural gas. Some work recently has been done to combine this crosslinking technology with wood-filled polyethylene. 

Figure 6.2 Variation of density, through the thickness of a 22 mm wall HDPE pipe.

The lifetime of a structure, under a constant load or stress, can be calculated if we know (i) The initial crack size and location, (ii) the Kj versus crack length relationship and (iii) the variation in the crack velocity V with Ki. This will be illustrated for an elliptical-shaped surface crack at the bore of an HDPE pipe under internal pressure p. The crack plane is normal to the hoop stress cth, while its ellipse minor axis a is perpendicular to, and major axis b parallel to, the bore. The stress intensity factor of such a crack is given by Ewalds and Wanhill (1984) as... 

Figure I 3.2 Extrusion method of making twin-walled corrugated HOPE pipe (from Diez C, Characteristics of Corrugated HDPE pipe, 7th Ed. 2005, Inc, Quebec,).

Problem 3 An HDPE pipe, for which the tensile creep data is given in Fig. 7.6, must have a hoop creep strain less than 3% after 50 years. If the gas pressure is 4 bai calculate the maximum SDR that can be used. 

Polyolefin floor coverings (of PP and PE), power cables with PE coverings and HDPE pipes and wall-covering materials, halogen-free LLDPE and crosslinked PE (XLPE) are all suggested as potential alternatives to PVC by Greenpeace [6]. 

Corrugated HDPE pipes are used in mortar, walls and concrete. 

Thiosynergist 29598-76-3 Naugard 412S 1162 47 P High-performance thiosynergist with LTHA in filled PR and PP and HDPE pipe... 

The development of improved performance HDPE pipe resins by the so-called inverse process, incorporating the comonomer in the high molar mass (not possible with Ziegler-type catalysts in a single reactor) is also an excellent example of design through dual reactor and multiple catalyst technologies. 

Fig. 7 Analysis of a HDPE pipe resin by GPC FTIR. SCB short chain branches, TC total number of carbon atoms [37]...

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